1. Field of the Invention
This invention relates to an apparatus for separating luminance and chrominance components in a composite video signal, which is suited to be used in a chromakey effect system.
2. Description of the Prior Art
A prior art luminance/chrominance separating apparatus (hereinafter referred to as "Y/C separating apparatus") includes, in combination, a vertical direction filter and a horizontal direction filter. The vertical direction filter performs the separation by utilizing a time-space correlation in the vertical direction of the composite video signal and the phase relationship of a chrominance signal (color subcarrier) between adjacent lines. The horizontal direction filter makes the separation by use of a low pass filter and a subtractor on the basis of the frequency distribution of the liminance and chrominance components of the composite video signal. The separation result obtained by the horizontal direction filter is delayed in order to match its timing with that of the separation result obtained by the vertical direction filter. This is because the vertical direction filter performs a vertical time-space correlation, which requires a delay of at least one horizontal line period. Thus, a time delay is unavoidably exhibited by the overall separation output of the prior art Y/C separating apparatus. Moreover, the prior art device requires a delay circuit for delaying the output of the horizontal direction filter to equalize the timing of the outputs of the two filters. Where the Y/C separation result is used independently of other circuits, no problem arises due to this time delay. However, where the Y/C separation result is to be used for controlling further processing of the video signal from which the Y/C separation has been obtained, it is necessary to provide yet another delay circuit in the transmission line of the video signal in order to compensate for the time delay of the Y/C separation circuit. For example, this problem arises when a chromakey effect is to be performed with a composite video signal, in which case an additional delay circuit is required in the transmission line for the composite video signal.